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Make optional type narrowing actually optional in tuples_type_compat.py #1981

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erictraut merged 1 commit into from
Apr 22, 2025
Merged

Make optional type narrowing actually optional in tuples_type_compat.py #1981

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16 changes: 8 additions & 8 deletions conformance/tests/tuples_type_compat.py
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Original file line number Diff line number Diff line change
Expand Up @@ -71,15 +71,15 @@ def func4(
def func5(val: tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int]):
if len(val) == 1:
# Type can be narrowed to tuple[int].
assert_type(val, tuple[int]) # tuple[int]
assert_type(val, tuple[int]) # E?: tuple[int]
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@JelleZijlstra JelleZijlstra Apr 22, 2025

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This makes the test not very useful (without manual review) since type checkers will now pass no matter what type they infer for val. One solution could be to use two types and asserts that exactly one of them errors, by using an error group and asserting for both the narrowed and non-narrowed type. However, we don't currently check in that case that there is exactly one error. I can send a PR doing that.

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@missingdays missingdays Apr 22, 2025

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Sounds reasonable to me.


if len(val) == 2:
# Type can be narrowed to tuple[str, str] | tuple[int, int].
assert_type(val, tuple[str, str] | tuple[int, int])
assert_type(val, tuple[str, str] | tuple[int, int]) # E?

if len(val) == 3:
# Type can be narrowed to tuple[int, str, int].
assert_type(val, tuple[int, str, int])
assert_type(val, tuple[int, str, int]) # E?


# > This property may also be used to safely narrow tuple types within a match
Expand All @@ -92,15 +92,15 @@ def func6(val: tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int])
match val:
case (x,):
# Type can be narrowed to tuple[int].
assert_type(val, tuple[int]) # tuple[int]
assert_type(val, tuple[int]) # E?: tuple[int]

case (x, y):
# Type can be narrowed to tuple[str, str] | tuple[int, int].
assert_type(val, tuple[str, str] | tuple[int, int])
assert_type(val, tuple[str, str] | tuple[int, int]) # E?

case (x, y, z):
# Type can be narrowed to tuple[int, str, int].
assert_type(val, tuple[int, str, int])
assert_type(val, tuple[int, str, int]) # E?


# > Type checkers may safely use this equivalency rule (tuple expansion)
Expand All @@ -112,9 +112,9 @@ def func6(val: tuple[int] | tuple[str, str] | tuple[int, *tuple[str, ...], int])
def func7(subj: tuple[int | str, int | str]):
match subj:
case x, str():
assert_type(subj, tuple[int | str, str])
assert_type(subj, tuple[int | str, str]) # E?
case y:
assert_type(subj, tuple[int | str, int])
assert_type(subj, tuple[int | str, int]) # E?


# > The tuple class derives from Sequence[T_co] where ``T_co`` is a covariant
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